The band's songwriting team of Eddie Brigati and Cavaliere then began providing most of their songs, and the hits kept coming for two years. Their immediate follow-ups to "Good Lovin'", including "You Better Run" (1966; covered in 1980 by Pat Benatar) and "Come On Up" were only modest hits. "(I've Been) Lonely Too Long" (1967) did better, and "Groovin'"[4] (#1 US/Canada, 1967) returned them to the top of the charts. They reeled off a succession of top 20 US hits, including "A Girl Like You" (1967), "How Can I Be Sure" (1967), "It's Wonderful" (1968), and "A Beautiful Morning" (1968). The band was exceptionally popular in Canada where "A Girl Like You", "How Can I Be Sure?", and "A Beautiful Morning" all reached #1. But they struggled in the UK, where they only twice reached the top 75, with "Groovin'" (#8) and "A Girl Like You" (#35). The band would bill themselves as the Young Rascals for the last time with the single release of "It's Wonderful"; they were known thenceforwards as simply 'the Rascals'.

Bruce Eder, writing for AllMusic, rates the band's 1967 album Groovin' as their best, noting the record's soulful core and innovative use of jazz and Latin instrumental arrangements. 1968's Once Upon A Dream was the first Rascals album designed from conception as an album, rather than as a vehicle to package their singles (eight of Groovin''s eleven songs had been released as single A or B sides, most in advance of the album). Once Upon a Dream, which peaked at #9 on the album charts, contained the single "It's Wonderful" plus many other strong songs, including "Easy Rollin'," "Rainy Day," "My World," and the title track. Perhaps understandably, the album's song "My Hawaii" became a top of the charts hit in Hawaii.

"A Ray of Hope", "Heaven", "See", and "Carry Me Back" were all modest U.S. hits for the band during late 1968 and 1969; all entered the top 40, but none higher than #24. In Canada, however, the Rascals were still major stars; all these songs went top ten, completing a run of 11 straight Canadian top ten hits for The Rascals from 1967 to 1969. December 1969's "Hold On" broke the run of top 40 US singles for the Rascals, stalling at #51, as well as the run of Canadian top tens, peaking at #22.

During their period of greatest celebrity, the band's influence on aspiring R & B-flavored white acts was without equal, especially in the northeastern U.S. Notable bands that incorporated (sometimes to the point of parody) the Rascals' full-on stage demeanor and energy as well as the intense, hyper-dramatic vocalizing, drumstick-spinning gyrations and heavy bottom-end rhythm also achieved some prominence: the Vagrants (featuring Leslie West, later of Mountain), and the epitome of over-the-top funky psychedelia, the Vanilla Fudge, all owed their styles to the Rascals' synthesis of show-biz and soul.

Brigati left the group in 1970, followed by Cornish in 1971. Their last Rascals album was Search and Nearness (#198 U.S.), which featured Brigati's lead vocals on the Cornish-penned "You Don't Know" and a cover of The Box Tops' hit "The Letter", and drummer Danelli's composition "Fortunes". The only single release from the album to chart was the spiritually themed "Glory, Glory" (#58 U.S., #40 Canada), with backing vocals by The Sweet Inspirations. Search and Nearness would be the Rascals' last album for Atlantic Records, with Cavaliere and Danelli taking the band to Columbia Records in mid-1971.

Cavaliere shifted towards more jazz- and gospel-influenced writing for the Rascals' next two albums, Peaceful World (U.S. #122) and The Island Of Real (U.S. #180), using Robert Popwell and Buzzy Feiten on bass and guitar respectively, and new singers Annie Sutton and Molly Holt. These albums didn't sell as well as their earlier work, with none of their associated singles reaching higher than #95 on the U.S. chart. Towards the end of 1970 Danny Weis (previously with Rhinoceros and Iron Butterfly) then joined as a replacement for Feiten on guitar and Feiten then again replaced Weis before the group disbanded.

Cavaliere released several solo albums during the 1970s. Brigati, with his brother David, released Lost in the Wilderness in 1976. Cornish and Danelli worked together in Bulldog, who released two albums — one for MCA Records in 1973, the second for Buddah in '74 — and Fotomaker, who issued three albums on Atlantic in 1978-79. In 1982, Danelli joined Steve Van Zandt in Little Steven and the Disciples of Soul for the group's first two albums.

After appearing at Atlantic Records 40th Anniversary Celebration on May 14, 1988, the Rascals reunited (with Cavaliere, Cornish, and Danelli) for a brief reunion tour in 1988; Eddie Brigati opted not to participate. The reunion group featured an expanded lineup that included Mel Owens (in Brigati's place) on vocals and percussion, Steve Mackey on bass, Ed Mattey on guitar, Dena Iverson on backup vocals and a horn section from Nashville to beef up the sound. The reunion did not last beyond the end of the year.

After that, Cavaliere returned to his solo career and in the 1990s there were two factions touring: The New Rascals (featuring Cornish and Danelli) and Cavaliere, who sometimes called his grouping Felix Cavaliere's Rascals. The New Rascals lasted only a short time but toured again in 2006 with two new members, Bill Pascali (formerly of Vanilla Fudge) on vocals and keyboards and Charlie Souza on bass and vocals. The New Rascals released a concert DVD, shot at club Centro in New Jersey on Route 35.

In early 2009, Eddie Brigati went on to put together a project of young musicians who played all the classics. Eddie performed with the group along with his brother David. Called The Boys From The Music House, the band consisted of 4 talented young boys from New Jersey. Anthony Duke Claus, a cousin of Eddie's, sang lead vocals and played tambourine, Joseph Pomarico played lead guitar, harmonica and sang background vocals. Adam Sullivan played the piano and the classic organ along with singing some background vocals, and Matt Gazzano played the drums.

The Rascals performing "Groovin'" during one of their 2013 Once Upon a Dream shows. The large video screen helped accentuate song themes and also showed interviews with members and re-enactments of the group's history. Left to right, Gene Cornish, Felix Cavaliere, Dino Danelli, Eddie Brigati, and various supporting players and singers.

The group's original lineup reunited for their first public performances in over 40 years with The Rascals: Once Upon a Dream, a combination concert/theatrical event that was produced and directed by Steven Van Zandt and Maureen Van Zandt with lighting/projection by Marc Brickman. In addition to the concert experience, the history of The Rascals, and the history of the 1960s through their music, is a combination of interviews with the four Rascals, filmed scenes of actors enacting key moments in the band's history, news footage, and archival footage of the band. The show originally ran for six performances in December 2012 at the Capitol Theatre in Port Chester, New York.

Fifteen performances of the show were subsequently delivered from April 15 to May 5, 2013 at the Richard Rodgers Theatre on Broadway in New York City.[6][7] Near the end of the show's Broadway run, it was announced that Once Upon a Dream would be taken on the road, with performances scheduled in various cities on the East coast of North America during May–December 2013.[8]

Following its national tour, the show was expected to return to Broadway for a second three-week limited-run from December 2013 through January 2014, at the Marquis Theatre, but was canceled.[9]

The Rascals were inducted into the Rock and Roll Hall of Fame on May 6, 1997. Steve Van Zandt gave the induction speech and presented the award. For the first time in years, all four original members appeared together. For their jam session (including David Brigati), they performed "Good Lovin'", "Groovin'", "How Can I Be Sure?", and "People Got To Be Free".[10]